Known cutting inserts for use with such metal cutting tools are formed with top and bottom faces and front and side relief flanks, with a cutting edge defined between the intersection of the front relief flank and the top face, the top face including a rake surface and chip forming means for suitably shaping and diverting the chips formed during the cutting operation so as to facilitate the breakage and removal thereof without damage to the workpiece and cutting tool and without danger to the tool operator.
The chip forming means are generally designed to narrow the chip, so as to ensure that in grooving or parting operations the chip flows smoothly through the cutting region and also, to some extent, to rigidize the chip so as to facilitate its subsequent deflection and compacting in spiral form and eventual breakage.
It will be realised that the entire process of chip forming, shaping and deflection, involving as it does the continuing abutment in movement of the chip with the chip forming means, is accompanied by forces which tend to resist the movement of the chip and, in order to overcome these forces, the cutting operations are accompanied by increased power requirements. There is, therefore, in consequence a relatively increased generation of heat during the cutting operation which leads to an increased heating, on the one hand, of the cutting insert and cutting tool and, on the other hand, of the workpiece.
Whilst such increased heating of the cutting insert may itself lead to increasing wear of the cutting insert and necessitate its frequent replacement, the increased heating of the workpiece can be particularly undesirable in the case of workpieces made of stress hardening materials, i.e. materials wherein excessive heating leads to the generation of undesirable stresses and these stresses, in their turn, lead to an undesirable hardening of the material. Thus, with such stress hardening materials (examples of which include stainless steel and so-called space alloys), the hardening of the material as a result of heat-induced stresses generated during an initial cutting operation, results in the hardening of the material, rendering the subsequent cutting operation more difficult, with a greater power requirement.
Thus, with such stress hardening materials, efforts should be directed in the design of the cutting tool to ensure that the cutting operation is accompanied by a minimum amount of heat and, in this connection, the heat generated during the chip forming should be reduced to a minimum.
It is known, in this connection, that the more highly positive is the cutting edge, the less heat is generated. It is, however, not possible to render the cutting edge unduly highly positive, seeing that this inevitably results in an undesirable weakening of the cutting edge and requiring its frequent replacement. The use of low feed rates, on the other hand, results in the formation of relatively thin chips and it is known that with such relatively thin chips special chip forming means have to be provided in order to ensure the effective shaping and disposal of these thin chips.